The use of pedicle screw fasteners is well known for their use with spinal fixation systems. In the field of spinal pathologies, spinal fixation systems represent a major medical breakthrough. Surgically implanted fixation systems are commonly used to correct a variety of back structure problems, including those which occur as a result of trauma or improper development during growth. A commonly applied fixation system includes the use of one or more stabilizing rods aligned in a desired orientation with respect to a patient's spine. The pedicle screw provides anchoring of the fixation system wherein a series of connectors are used to rigidly link rods and the anchors.
Common to all spinal implant systems is the necessity for proper anchoring to the bone so as to provide support for the aforementioned components. The use of a polyaxial design pedicle screw has proven very effective in allowing a surgeon the flexibility to secure an installation with minimal strain on the individual. However, one of the problems with a polyaxial pedicle screw is the lack of a stabilized angular placement position during installation. Once a polyaxial pedicle screw is inserted into the bone, the connector component portion has yet to receive a connecting rod leaving the connector assembly to flop over making it difficult for the Surgeon to grasp while in the midst of surgery. This problem is compounded by the need to align multiple component heads for receipt of a connecting rod. Another problem with the prior art is the inability to use various size anchoring screw in combination with a common saddle larger saddle, both of which leads to assembly integrity over a large range of installation considerations.
A conventional polyaxial bone screw typically consists of a single shaft with a coarse thread at one end for threading into the bone. A spherical ball is positioned at an opposite end for coupling to a connecting member. For example, a number of patents exist for bone screw anchoring assemblies that include a U-shaped connector element which acts as a saddle for attachment to an alignment rod. U.S. Pat. No. 5,133,717 sets forth a sacral screw with a saddle support. Disclosed is the use of an auxiliary angled screw to provide the necessary support in placing the screw in an angular position for improved anchoring.
U.S. Pat. No. 5,129,900 sets forth an attachment screw and connector member that is adjustably fastened to an alignment rod. An oblong area provided within each connector member allows minute displacement of the alignment rod.
U.S. Pat. No. 4,887,595 discloses a screw that has a first externally threaded portion for engagement with the bone and a second externally threaded portion for engagement with a locking nut. The disclosure illustrates the use of a singular fixed shaft.
U.S. Pat. No. 4,946,458 discloses a screw which employs a spherical portion which is adapted to receive a locking pin so as to allow one portion of the screw to rotate around the spherical portion. A problem with the screw is the need for the locking pin and the inability of the base screw to accommodate a threaded extension bolt.
U.S. Pat. No. 5,002,542 discloses a screw clamp wherein two horizontally disposed sections are adapted to receive the head of a pedicle screw for use in combination with a hook which holds a support rod at an adjustable distance.
U.S. Pat. No. 4,854,304 discloses the use of a screw with a top portion that is adaptable for use with a specially designed alignment rod to permit compression as well as distraction.
U.S. Pat. No. 4,887,596 discloses a pedicle screw for use in coupling an alignment rod to the spine wherein the screw includes a clamp permitting adjustment of the angle between the alignment rod and the screw.
U.S. Pat. No. 4,836,196 discloses a screw with an upper portion designed for threadingly engaging a semi-spherical cup for use with a specially designed alignment rod. The alignment rod includes spaced apart covertures for receipt of a spherical disc allowing a support rod to be placed at angular positions.
U.S. Pat. No. 5,800,435 sets forth a modular spinal plate assembly for use with polyaxial pedicle screw implant devices. The device includes compressible components that cooperatively lock the device along included rails.
U.S. Pat. No. 5,591,166 discloses an orthopedic bone bolt and bone plate construction including a bone plate member and a collection of fasteners. At least one of the fasteners allows for multi-angle mounting configurations. The fasteners also include threaded portions configured to engage a patient's bone tissue.
U.S. Pat. No. 5,569,247 discloses a multi-angle fastener usable for connecting patient bone to other surgical implant components. The '247 device includes fastening bolts having spherical, multi-piece heads that allow for adjustment during installation of the device.
U.S. Pat. No. 5,716,357 discloses a spinal treatment and long bone fixation apparatus. The apparatus includes link members adapted to engage patient vertebrae. The link members may be attached in a chain-like fashion to connect bones in a non-linear arrangement. The apparatus also includes at least one multi-directional attachment member for joining the link members. This allows the apparatus to be used in forming a spinal implant fixation system.
Another type of spinal fixation system includes rigid screws that engage the posterior region of a patient's spine. The screws are designed with rod-engaging free ends to engage a support rod that has been formed into a desired spine-curvature-correcting orientation. Clamping members are often used to lock the rod in place with respect to the screws. Instead of clamping members, other fixation systems, such as that disclosed in U.S. Pat. No. 5,129,900 employs connectors that join the support rods and anchoring screws. The connectors eliminate unwanted relative motion between the rod and the screws, thereby maintaining the patient's spine in a corrected orientation.
Other spinal fixation systems employ adjustable components. For example, U.S. Pat. No. 5,549,608 includes anchoring screws that have pivoting free ends which attach to discrete rod-engaging couplers. As a result, the relative position of the anchoring screws and rods may be adjusted to achieve a proper fit, even after the screw has been anchored into a patient's spinal bone. This type of fixation system succeeds in easing the rod-and-screw-linking process. This adjustment capability allows the screws to accommodate several rod paths.
U.S. Pat. No. 7,445,627 discloses a fastener and a bone fixation assembly for internal fixation of vertebral bodies. According to one exemplary embodiment, a tulip assembly is employed; the tulip assembly includes a non-circular surface disposed on its outer surface. A fastener is coupled to the tulip assembly and positionable to retain the tulip assembly on the head of a screw. A cap having an outer surface and a plurality of inner protrusions mateably connects to the non-circular surface on the tulip body to compress the tulip assembly to secure a rod.
U.S. Publication No. 2008/0177322 discloses a spinal stabilization system that includes bone fastener assemblies that are coupled to vertebrae. Each bone fastener assembly includes a bone fastener and a collar. The bone fastener has a head portion having at least a first cross-sectional shape in a first plane, and a second cross-sectional shape in a second plane. The collar has a circular opening in the bottom, with a relief extending from the circular opening. The second cross-sectional shape of the bone fastener is keyed to the opening to permit insertion of the bone fastener into the collar assembly from the bottom. After insertion, the bone fastener is rotated to prohibit removal of the bone fastener from the collar. The collar can then be rotated and/or angulated relative to the bone fastener. An elongated member can be positioned in the collar and a closure member is then used to secure the elongated member to the collar.
U.S. Publication No. 2006/0241599 discloses a polyaxial fixation device having a shank with a spherical head formed on a proximal end thereof, and a receiver member having an axial passage formed therein that is adapted to polyaxially seat the spherical head of the shank. The polyaxial bone screw further includes an engagement member that is adapted to provide sufficient friction between the spherical head and the receiver member to enable the shank to be maintained in a desired angular orientation before locking the spherical head within the receiver member.
U.S. Publication No. 2006/0235392 discloses a system for connecting a fastener element (e.g., a pedicle screw) relative to a rod for the purposes of vertebral fixation. The system may permit multi-axial movement between the fastener element and the rod. Further, the system may permit the angular relationship between the fastener element and the rod to be held in a desired orientation.
U.S. Publication No. 2006/0155277 discloses an anchoring element for securing a rod on a vertebra, that comprises a retaining means for receiving the rod, a safety element placed on the retaining means, a securing element which can be placed on the body of the vertebra, and a clamping device which is arranged between the retaining means and the securing element. The clamping device includes a ring-shaped mount, a partially conical-segment shaped bearing and an intermediate element which is embedded in the mount and which engages the bearing, whereby the mounting is moveable in a removed state in relation to the bearing, whereas the mount is maintained in a clamped state on the bearing by means of the intermediate element. The mount is rigidly connected to the retaining means and the bearing is rigidly connected to the securing element.
U.S. Publication No. 2006/0149240 discloses a polyaxial bone screw assembly that includes a threaded shank body having an upper capture structure, a head and a multi-piece retainer, articulation structure. The geometry of the retainer structure pieces correspond and cooperate with the external geometry of the capture structure to frictionally envelope the retainer structure between the capture structure and an internal surface defining a cavity of the head. The head has a U-shaped cradle defining a channel for receiving a spinal fixation or stabilization longitudinal connecting member. The head channel communicates with the cavity and further with a restrictive opening that receives retainer pieces and the capture structure into the head but prevents passage of frictionally engaged retainer and capture structures out of the head. The retainer structure includes a substantially spherical surface that mates with the internal surface of the head, providing a ball joint, enabling the head to be disposed at an angle relative to the shank body.
U.S. Pat. No. 6,716,214 discloses a polyaxial bone screw having a bone implantable shank, a head and a retaining ring. The retaining ring includes an outer partial hemispherical surface and an inner bore with radially extending channels and partial capture recesses. The shank includes a bone implantable body with an external helical wound thread and an upwardly extending capture structure. The capture structure includes at least one spline which extends radially outward and has a wedged surface that faces radially outward therefrom. The capture structure operably passes through a central bore of the retaining ring while the spline passes through a suitably shaped channel so that the spline becomes positioned above the head, at which time the shank is rotated appropriately and the shank is drawn back downwardly so that the spline engages and seats in the capture recess. The head includes an internal cavity having a spherical shaped surface that mates with the ring surface and has a lower restrictive neck that prevents passage of the ring once the ring is seated in the cavity.
U.S. Pat. No. 6,565,567 discloses a pedicle screw assembly for use with a rod for the immobilization of bone segments. The assembly is comprised of a screw, a polyaxial housing for receiving the screw, a washer, a set screw, and a cup-shaped cap. The lower portion of the housing terminates in a reduced cross-sectional area, which engages the bottom of the screw head. When the screw is placed inside the polyaxial housing and the screw is secured into the bone, the polyaxial housing is pivotable with three degrees of freedom. The housing includes a top portion with a pair of upstanding internally threaded posts. A washer is inserted between the head of the screw and the rod. A cap, having a bottom, with a pair of posts accommodating openings and a lateral cross connector, is placed over the posts so that the cross connector engages the rod. The cross connector and washer have concave generally semi-cylindrical rod engaging surfaces to prevent the rod from rotating or sliding within the housing once the set screw is tightened. A set screw is threaded into the housing posts to secure the rod within the housing. The washer has a roughened lower surface which, in conjunction with the reduced cross-sectional area at the bottom of the housing, securely clamps and locks the housing to the screw head when the set screw is tightened.
U.S. Pat. No. 5,501,684 discloses an osteosynthetic fixation device which consists of a fixation element which has a conical head section and an anchoring element abutting it which is for attachment into the bone. The fixation device also consists of a spherically formed, layered, slotted clamping piece which has a conical borehole for installation of the conical head section, and which is meant for locking within a connecting piece equipped with a spherically shaped layered borehole. Fixation piece has an axially arrayed tension element, permitting axial displacement and wedging of conical head section in the borehole that corresponds with it. The fixation device is appropriate for use as a plate/screw system, an internal or external fixator, and in particular for spinal column fixation.
U.S. Pat. No. 4,693,240 discloses a bone pin clamp for external fracture fixation. The apparatus comprises rotation, slide and housing elements nested one within the next, each such element having an aperture to receive a pin therethrough, and the rotation and slide elements respectively affording pin adjustment in azimuth and zenith, and in height, relative to the housing element. A locking mechanism including a common actuator member is operable simultaneously to lock the pin and rotation and slide elements in the housing element. In a preferred form, the housing element serves as a cylinder with the slide element as a keyed piston therein, and the rotation element is a disc located between a screw and annular thrust members engaged in the piston, the piston and disc being split respectively to lock by expansion and compaction under screw action towards the thrust members.
U.S. Pat. No. 4,483,334 discloses an external fixation device for holding bone segments in known relation to each other. The device includes a pair of bone clamp assemblies each secured to bone pins extending from the bone segments, a bridge extending between the pin clamp assemblies, and a specialized high friction universal assembly connecting the bridge to each of the pin clamp assemblies.
U.S. Pat. No. 4,273,116 discloses an external fixation device for reducing fractures and realigning bones that includes sliding universal articulated couplings for enabling easy adjustment and subsequent locking of connections between Steinmann pins and tubular tie-rods. The couplings each include a split, spherical adapter sleeve which is embraced by the matching inner surface of an open ring portion of a coupling locking clamp having clamp lugs tightenable against a block by means of a nut-and-bolt assembly. Further nut-and-bolt assemblies are disposed in elongated slots in the blocks and cooperate with associated clamping members to clamp the Steinmann pins to the blocks after adjustment in two orthogonal directions and optional resilient bending of the pins.
U.S. Pat. No. 6,672,788 discloses a ball and socket joint incorporating a detent mechanism that provides positive biasing toward a desired position. The ball and socket joint can be used in flexible supports that hold and support items such as lamps, tools and faucets. The detent mechanism comprises two corresponding parts, one in the ball portion and the second in the socket portion of the joint. The first detent part is a protrusion of some type and the second detent part is a groove or indentation that is adapted to accept and engage the protrusion. If the ball contains the detent protrusion, then the socket contains the detent indentation. And conversely, if the socket contains the detent protrusion, then the ball contains the detent indentation. The detent tensioning force can be provided by a spring or a spring band, the characteristics of the material from which the joint is made, or by some other similar tensioning device.
U.S. Publication No. 2003/0118395 discloses a ball and socket joint, which has a housing, a ball pivot mounted pivotably in the housing, and a sealing bellows, which is fastened to the housing and is mounted on the ball pivot slidably via a sealing ring provided with two legs. A first leg of the two legs is in contact with the ball pivot under tension and the second leg meshes with the wall of the sealing bellows. The second leg is, furthermore, fastened in an anchoring ring arranged at least partially in the wall of the sealing bellows.
U.S. Pat. No. 4,708,510 discloses a ball joint coupling assembly that permits universal movement and positioning of an object with respect to a vertical support shaft. Quick release/lock action is provided by a ball joint assembly having a housing in which a ball and piston are movably coupled. The ball is captured between annular jaw portions of the housing and piston, with locking action being provided by gripping engagement of the piston jaw portion and the housing jaw portion. The ball member is gripped in line-contact, compressive engagement by the annular edges of the piston jaw and housing jaw on opposite sides of the ball. The piston is constrained for axial movement within the housing with locking engagement and release being effected by rotation of a threaded actuator shaft.
U.S. Pat. No. 3,433,510 discloses a swivel structure for rigidly joining first and second parts together. A first member is connected to the first part and a second member is connected to the second part. An intermediate hollow member interconnects the first and second members together. An enlarged outer end portion is provided on the first member and includes a plurality of locking means thereon. Means are provided on the second member for engaging one of the locking means. Means are provided for threadably joining the hollow member and the second member together. A slot is provided in the hollow member and includes an enlarged entrance which passes the enlarged outer end portion and which also includes a restricted opening opposite the threaded joining of the hollow member and the second member together. The portion surrounding the restricted opening opposes the forces imparted against the outer end portion as the second member is threadably joined to the hollow portion and bears against the outer end portion.
U.S. Patent Publication No. 2008/0269809 discloses a bottom loading pedicle screw assembly. The device includes a pedicle screw and a connector member. The pedicle screw includes a threaded lower portion while the upper portion includes a groove sized to accept a clip member. The clip member includes a spherical outer surface. In operation the clip is placed within the groove and the assembly is pressed through the opening in the bottom of the connector member. While the device is bottom loading, the device will separate when the pedicle screw is aligned with the connector member. The construction of the clip member allows the clip to collapse sufficiently to pass back through the opening when the screw is positioned in alignment with the connector, requiring the connection to bone be placed at an angle with respect to the connector for proper operation.
Thus, what is needed is a polyaxial pedicle screw system that can be adapted for use in a spinal fixation system that includes a thread thru assembly allowing different sized anchoring screws to be coupled to a single size connector, and an assembly that maintains the connector member in position to assist a surgeon during installation.